A mobile phone subscriber may be charged a fee to send or receive a Short Message Service (SMS) message. Additionally, the subscriber may be charged an additional fee for a Premium SMS (PSMS) message. For a post-pay subscriber, these fees may accrue during and become due at the end of the billing cycle (e.g., monthly, quarterly, on a specific date, etc.). As a result, a post-pay subscriber is typically not required to have sufficient funds in an account (or on a phone card, etc.) at the time of message sending or delivery in order to pay for any SMS or Premium SMS charges that may be assessed.
However, a pre-pay mobile phone subscriber typically pays for service before use (e.g., through purchase of a pre-paid phone card), and may not be subject to future billing. To facilitate payment of any SMS/PSMS charges from such a subscriber, the SMS/PSMS charges may be debited from the subscriber's account (e.g., from the subscriber's pre-paid phone card) at or near the time of SMS/PSMS message sending or delivery.
If insufficient funds remain in the pre-pay subscriber's account, then the sending or delivery of SMS/PSMS messages may be blocked. Additionally, SMS/PSMS messages may be blocked for both pre-pay and post-pay subscribers who have some or all SMS/PSMS services restricted.